Semiconductor memory device comprising magneto resistive element and its manufacturing method

ABSTRACT

A semiconductor memory device includes a memory cell, a side wall insulating film, and an interlayer insulating film. A memory cell includes a first ferromagnetic film, a tunnel barrier film formed on the first ferromagnetic film, and a second ferromagnetic film formed on the tunnel barrier film. The side wall insulating film is formed so as to surround at least sides of the second ferromagnetic film. The interlayer insulating film is formed so as to cover the memory cell and the side wall insulating film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Applications No. 2003-080586, filed Mar. 24,2003; and No. 2003-207564, filed Aug. 14, 2003, the entire contents ofboth of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor memory device and itsfabricating method, e.g. a magneto resistive element provided in amagneto resistive random access memory (MRAM) and its peripheralstructure.

2. Description of the Related Art

The MRAM is a general term for solid state memories which act asrecorded information carriers utilizing the direction of magnetizationof ferromagnetic material and which enable recorded information to berewritten, retained, and read as required.

A memory cell in the MRAM normally has a structure in which a pluralityof ferromagnetic materials are stacked together. Information is recordedby using binary information “1” and “0” to represent the relativearrangement of magnetizations of the plurality of ferromagneticmaterials in the memory cell, i.e. to indicate whether the directions ofthe magnetization are parallel or antiparallel with one another.Recording information is written to the memory by using current magneticfields to reverse the directions of magnetization of ferromagneticmaterials of each memory cell.

The MRAM is perfectly nonvolatile and enables information to berewritten 10¹⁵ times or more. Furthermore, the MRAM enablesnondestructive reading and does not require any refresh operations.Accordingly, it enables a read cycle to be reduced. It is also resistantto radiations compared to charge accumulation type memory cells. Thus,the MRAM has a large number of advantages in terms of functions comparedto conventional semiconductor memories using dielectrics. The degree ofintegration per unit area of the MRAM and the time required by the MRAMfor a write or read are expected to be generally equivalent to those ofa DRAM (Dynamic Random Access Memory). Accordingly, the non-volatilityof the MRAM, its major characteristic, is expected to be utilized to useit as an external storage device for portable equipment, embedding it inan LSI, or apply it to a main memory of a personal computer.

An MRAM that is now examined so as to be put to practical use uses amagnetic tunnel junction (hereinafter simply referred to as an “MTJ”)for the memory cell. Such an example is described in, for example, “IEEEInternational Solid-State Circuits Conference 2000 Digest Paper”, TA7.2.The MTJ mainly comprises a three-layer film including a ferromagneticlayer, an insulating layer, and a ferromagnetic layer. A current tunnelsthe insulating layer. The resistance value of the junction varies inproportion to the cosine of the relative angle between the directions ofmagnetization in both ferromagnetic metal layers. The resistance valueof the junction is largest when the directions of magnetization in bothferromagnetic layers are antiparallel with each other. This is a tunnelmagneto resistive effect. One type of MTJ has a structure that retainsdata utilizing a difference in magnetic coercive force between bothferromagnetic materials. Another type of MTJ has a so-called spin valvestructure in which an antiferromagnetic material is arranged adjacent toone of the ferromagnetic materials to pin the directions ofmagnetization. The spin valve structure aims reduction of write currentand improve the magnetic field sensitivity. An MRAM having the spinvalve structure is described in, for example, “Japanese Journal ofApplied Physics”, 1997, No. 36, p. 200.

A brief description will be given of a conventional method of forming anMTJ element having the spin valve structure.

First, a switching transistor is formed on a semiconductor substrate.Subsequently, an interlayer insulating film, a local interconnect layer,a write interconnect layer, and a contact plug are formed in this order.Then, a nonmagnetic conductive film is formed on the interlayerinsulating film as a leading interconnect layer.

Next, a ferromagnetic layer is formed on the leading interconnect layeras a pinning layer. Furthermore, an insulating layer is formed on thepinning layer as a tunnel barrier film. Subsequently, a ferromagneticlayer is formed on the tunnel barrier film as a free layer.

Moreover, the free layer, the tunnel barrier film, and the pinning layerare patterned using a photolithography technique and ion milling. Thiscompletes an MTJ element.

Next, an SiO₂ film is formed on the MTJ element in order to protect theMTJ element. Then, the SiO₂ film and the nonmagnetic conductive film arepatterned using the photolithography technique and etching. Thiscompletes a leading interconnect layer.

Subsequently, an interlayer insulating film is formed so as to cover theMTJ element. Furthermore, a contact plug is formed in the interlayerinsulating film so as to reach the free layer.

The MTJ element is formed as described above.

However, in the conventional MRAM, the upper and lower ferromagneticlayers, arranged opposite each other via the tunnel barrier film, may beelectrically short-circuited at their ends. Thus, the yield of the MRAMdecreases significantly. This is mainly because when a junction isetched using ion milling, residue containing metal remains near thetunnel barrier at a certain probability. The tunnel barrier film has avery small thickness of about 1 to 1.5 nm. That is, the upper and lowersubstrates are adjacent to each other at a very small distance of 1 to1.5 nm. Thus, if the residue is larger than 1 to 1.5 nm in size, a shortcircuit may occur. However, for a large-scale MRAM, it is substantiallyimpossible to avoid this defect. As the degree of integration of theMRAM increases, it tends to become increasingly difficult to obtainacceptable products.

It is contemplated that the above short circuit problem may be solvedby, for example, allowing ions to be incident at about 45° during an ionmilling step. In this case, the sides of the MTJ are tapered. As aresult, the probability of occurrence of a defect is expected todecrease. However, in an MRAM of a Gbit class, an MTJ element has a sizeof, for example, 0.1×0.2 μm. The distance between adjacent MTJ elementsis about 0.1 μm. Then, to avoid an electric short circuit between theadjacent MTJ elements, ions are desirably allowed to enter the substratesurface as perpendicularly to it as possible during the ion millingstep. That is, the short circuit between the MTJ elements and the shortcircuit between the ferromagnetic layers are traded off with each other.

BRIEF SUMMARY OF THE INVENTION

A semiconductor memory device according to an aspect of the presentinvention comprises:

-   -   a memory cell comprising a first ferromagnetic film, a tunnel        barrier film formed on the first ferromagnetic film, and a        second ferromagnetic film formed on the tunnel barrier film;    -   a side wall insulating film formed so as to surround at least        sides of the second ferromagnetic film; and    -   an interlayer insulating film formed so as to cover the memory        cell and the side wall insulating film.

A method for fabricating a semiconductor memory device according to anaspect of the present invention comprises:

-   -   forming a first ferromagnetic layer on a semiconductor layer;    -   forming a tunnel barrier film on the first ferromagnetic layer;    -   forming a second ferromagnetic layer on the tunnel barrier film;    -   patterning the second ferromagnetic layer to expose a part of        the tunnel barrier film;    -   forming a side wall insulating film on the tunnel barrier film        so that the side wall insulating film surrounds side walls of        the second ferromagnetic layer; and    -   patterning the tunnel barrier film and the first ferromagnetic        layer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1A is a sectional view of an MRAM according to a first embodimentof the present invention;

FIG. 1B is a perspective view of the MRAM according to the firstembodiment of the present invention;

FIG. 1C is a flow chart of MRAM fabricating steps according to the firstembodiment of the present invention;

FIGS. 2A to 2L are sectional views sequentially showing the MRAMfabricating steps according to the first embodiment of the presentinvention;

FIG. 3 is a flow chart of MRAM fabricating steps according to a secondembodiment of the present invention;

FIGS. 4A and 4B are sectional views sequentially showing the MRAMfabricating steps according to the second embodiment of the presentinvention;

FIG. 5 is a flow chart of MRAM fabricating steps according to a thirdembodiment of the present invention;

FIGS. 6A to 6I are sectional views sequentially showing the MRAMfabricating steps according to the third embodiment of the presentinvention;

FIG. 7 is a flow chart of MRAM fabricating steps according to avariation of the third embodiment of the present invention;

FIG. 8 is a sectional view of a magneto resistive element provided in anMRAM according to a fourth embodiment of the present invention;

FIG. 9A is a plan view of an ideal magneto resistive element, showingthe orientations of spins;

FIG. 9B is a plan view of an actual magneto resistive element, showingthe orientations of spins;

FIG. 9C is a plan view of the magneto resistive element provided in theMRAM according to the fourth embodiment of the present invention;

FIG. 10 is a sectional view of a magneto resistive element provided inan MRAM according to a fifth embodiment of the present invention;

FIG. 11 is a plan view of the magneto resistive element provided in theMRAM according to the fifth embodiment of the present invention;

FIG. 12 is a sectional view of a magneto resistive element provided inan MRAM according to a sixth embodiment of the present invention;

FIG. 13 is a sectional view of a magneto resistive element provided inan MRAM according to a seventh embodiment of the present invention;

FIGS. 14A and 14B are sectional views sequentially showing MRAMfabricating steps according to the seventh embodiment of the presentinvention;

FIG. 15A is a sectional view of an MRAM according to an eighthembodiment of the present invention;

FIG. 15B is a perspective view of the MRAM according to the eighthembodiment of the present invention;

FIG. 15C is a flow chart of MRAM fabricating steps according to theeighth embodiment of the present invention;

FIGS. 16A to 16F are sectional views sequentially showing the MRAMfabricating steps according to the eighth embodiment of the presentinvention;

FIG. 17 is a flow chart of MRAM fabricating steps according to a ninthembodiment of the present invention;

FIGS. 18A and 18B are sectional views sequentially showing the MRAMfabricating steps according to the ninth embodiment of the presentinvention;

FIG. 19 is a flow chart of MRAM fabricating steps according to a tenthembodiment of the present invention;

FIGS. 20A to 20F are sectional views sequentially showing the MRAMfabricating steps according to the tenth embodiment of the presentinvention;

FIG. 21 is a flow chart of MRAM fabricating steps according to avariation of the tenth embodiment of the present invention;

FIG. 22 is a sectional view of a magneto resistive element provided inan MRAM according to an eleventh embodiment of the present invention;

FIG. 23 is a sectional view of a magneto resistive element provided inan MRAM according to a twelfth embodiment of the present invention;

FIG. 24 is a sectional view of a magneto resistive element provided inan MRAM according to a thirteenth embodiment of the present invention;

FIG. 25 is a plan view of a magneto resistive element provided in anMRAM according to the fourteenth embodiment of the present invention;

FIG. 26A is a flow chart of MRAM fabricating steps according to afifteenth embodiment of the present invention;

FIG. 26B is a flow chart of MRAM fabricating steps according to avariation of the fifteenth embodiment of the present invention;

FIG. 27 is a block diagram of a modem having the MRAM according to thefirst to fifteenth embodiments of the present invention;

FIG. 28 is a block diagram of a cellular phone having the MRAM accordingto the first to fifteenth embodiments of the present invention;

FIG. 29 is a block diagram of a card having the MRAM according to thefirst to fifteenth embodiments of the present invention;

FIG. 30 is a top view of a transfer device which transfers data of thecard having the MRAM according to the first to fifteenth embodiments ofthe present invention;

FIG. 31 is a sectional view of the transfer device which transfers dataof the card having the MRAM according to the first to fifteenthembodiments of the present invention;

FIG. 32 is a sectional view of a transfer device which transfers data ofthe card having the MRAM according to the first to fifteenth embodimentsof the present invention;

FIG. 33 is a sectional view of a transfer device which transfers data ofthe card having the MRAM according to the first to fifteenth embodimentsof the present invention;

FIG. 34 is a sectional view of a magneto resistive element provided inan MRAM according to a first modification of the first to fifteenthembodiment of the present invention; and

FIG. 35 is a sectional view of a magneto resistive element provided inan MRAM according to a first modification of the first to fifteenthembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1A, description will be given of a semiconductormemory device according to a first embodiment of the present invention.FIG. 1A is a sectional view of a memory cell in an MRAM.

As shown in this figure, an element isolating region STI is formed in asemiconductor substrate 10. A switching transistor 11 is formed in anelement area AA the periphery of which is surrounded by the elementseparating area STI. The switching transistor 11 comprises impuritydiffusion layers 12 formed in a surface region of the semiconductorsubstrate 10, a gate insulating film (not shown), and a gate electrode13. The gate electrode 13 functions as a word line and is formed like astripe extending along the direction of an easy axis (a directionperpendicular to the sheet of the drawing).

Further, an interlayer insulating film 14 is formed on the semiconductorsubstrate 10. The interlayer insulating film 14 covers the switchingtransistor 11. A contact plug 15 is formed in the interlayer insulatingfilm 14. The contact plug 15 is connected to one (a drain region) of theimpurity diffusion layers 12 of the switching transistor 11.

A metal interconnect layer 16 connected to the contact plug 15 is formedon the interlayer insulating film 14. Furthermore, an interlayerinsulating film 17 is formed on the interlayer insulating film 14. Theinterlayer insulating film 17 covers the metal interconnect layer 16. Acontact plug 18 is formed in the interlayer insulating film 17. Thecontact plug 18 is connected to the metal interconnect layer 16.

Metal interconnect layers 19 and 20 are formed on the interlayerinsulating film 17; the metal interconnect layer 19 is connected to thecontact plug 18, and the metal interconnect layer 20 is electricallyseparated from the metal interconnect layer. The metal interconnectlayer 20 functions as a write word line and is formed like a stripeextending along the direction of the easy axis. Furthermore, aninterlayer insulating film 21 is formed on the interlayer insulatingfilm 17. The interlayer insulating film 21 covers the metal interconnectlayers 19 and 20. A contact plug 22 is formed in the interlayerinsulating film 21. The contact plug 22 is connected to the metalinterconnect layer 19.

A nonmagnetic conductive film 23 connected to the contact plug 22 isformed on the interlayer insulating film 21. The nonmagnetic conductivefilm 23 functions as a leading interconnect layer. It is formed of amultilayer film including a Ta layer of, for example, film thickness 3nm, an Al layer 25 of, for example, film thickness 30 nm, and a Ta layer26 of, for example, film thickness 30 nm which are sequentially formed.Further, a magneto resistive element 27 is formed on the nonmagneticconductive film 23. The magneto resistive element 27 is formed to lie ontop of the metal interconnect layer 20 so as to sandwich the interlayerinsulating film 21 and the nonmagnetic conductive film 23 between itselfand the metal interconnect layer 20. The magneto resistive element 27 isdesigned so that an insulating film is sandwiched between magneticmaterial films and is, for example, an MTJ element.

The structure of the magneto resistive element 27 will be described withreference to FIGS. 1A and 1B. FIG. 1B is a perspective view of asemiconductor memory device focusing on the magneto resistive element27.

As shown in this figure, the magneto resistive element 27 is shaped likea general ellipse the major axis of which extends along the direction ofthe easy axis. The magneto resistive element 27 includes a pinning layer28 formed on the nonmagnetic conductive layer 23, a tunnel barrier film29 formed on the pinning layer 28, and a free layer 30 formed on thetunnel barrier film 29. The pinning layer 28 is formed of a stacked filmin which the following layers are sequentially formed: a seed layer (orbuffer layer) 31 formed of permalloy (Py: NiFe alloy) of, for example,film thickness 3 nm, an antiferromagnetic layer 32 formed of IrMn of,for example, film thickness 15 nm, and a pinning ferromagnetic layer 33formed of a CoFe layer of, for example, film thickness 5 nm. The tunnelbarrier film 29 is formed of an Al₂O₃ layer of, for example, filmthickness about 1 to 1.5 nm. The free layer 30 is formed of a stackedfilm including a CoFe layer 34 of, for example, 4 nm film thickness anda Py layer 35 of, for example, 20 nm film thickness which aresequentially formed.

The pinning layer 28 and the tunnel barrier film 29 have substantiallythe same surface area and completely overlap each other. The free layer30 has a smaller surface area than the pinning layer 28 and the tunnelbarrier film 29 and is provided, as a whole, on the tunnel barrier film29. The magneto resistive element 27 is thus formed.

A cap layer 36 is formed on the free layer 30. The cap layer 36 isformed of a multilayer film including a Ta layer of, for example, 20 nmfilm thickness, an Al layer 38 of, for example, 50 nm film thickness,and a Ta layer 39 of, for example, 10 nm film thickness which aresequentially formed. Further, a side wall insulating film 40 is formedon the tunnel barrier film 29 so as to surround at least the peripheryof the free layer 30. The side wall insulating film 40 is formed of, forexample, an Al₂O₃ film.

Further, an SiO₂ film 41 is formed on the nonmagnetic conductive film 23so as to cover the magneto resistive element 27, the cap layer 36, andthe side wall insulating film 40. The SiO film 41 serves to protect themagneto resistive element 27. Furthermore, an interlayer insulating film42 is formed on the interlayer insulating film 21 so as to cover thenonmagnetic conductive film 23 and the SiO₂ film 41. A contact plug 43is formed in the interlayer insulating film 42 and the SiO₂ film 41. Thecontact plug 43 extends from the surface of the interlayer insulatingfilm 42 to the Ta layer 39 in the cap layer 36. A bit line 44 connectedto the contact plug 43 is formed on the interlayer insulating film 42.

The memory cell including the magneto resistive element 27 and theswitching transistor 11 is formed as described above. Spins in thepinning layer 28 in the magneto resistive element 27 are set beforehandto have predetermined orientations. The orientations of spins in thefree layer 30 are then set to be parallel or antiparallel with thepinning layer 28. This creates two states to cause “0” or “1” data to bewritten in the magneto resistive element 27.

Now, with reference to FIGS. 1C and 2A to 2L, description will be givenof method of fabricating the semiconductor memory device shown in FIGS.1A and 1B. FIG. 1C is a flow chart of MRAM fabricating steps accordingto the present embodiment. FIGS. 2A to 2L are sectional viewssequentially showing the fabricating steps. In FIGS. 2B to 2L, thestructure including the metal interconnect layers 19 and 20 and othercomponents located below them is omitted.

First, in step S1 in FIG. 1C, the switching transistor 11 and thecontact plug are formed. That is, as shown in FIG. 2A, the elementisolating region STI is formed in the semiconductor substrate 10. Then,the switching transistor 11 is formed on the element area AA surroundedby the element isolating region STI using a well-known manner. The gateelectrode 13 of the switching transistor 11 is formed like a stripeextending along the direction of the easy axis. Then, the interlayerinsulating film 14 is formed on the semiconductor substrate 10. Theinterlayer insulating film 14 covers the switching transistor 11.Subsequently, the contact plug 15 is formed in the interlayer insulatingfilm 14. The contact plug 15 is connected to the drain region 12 of theswitching transistor.

Then, the metal interconnect layer 16 is formed on the interlayerinsulating film 14. The metal interconnect layer 16 is connected to thecontact plug 15. Then, the interlayer insulating film 17 is formed onthe interlayer insulating film 14. Subsequently, the contact plug 18 isformed in the interlayer insulating film 17. The contact plug 18 isconnected to the metal interconnect layer 16.

Then, the metal interconnect layers 19 and 20 are formed on theinterlayer insulating film 17. The metal interconnect layer 19 isconnected to the contact plug 18. The metal interconnect layer 20 isseparated from the metal interconnect layer 19 and is formed like astripe extending along the direction of the easy axis. It is locatedimmediately above the gate electrode 13. Subsequently, the interlayerinsulating film 21 is formed on the interlayer insulating film 17. Theinterlayer insulating film 21 covers the metal interconnect layers 19and 20. Subsequently, the contact plug 22 is formed in the interlayerinsulating film 21. The contact plug 22 is connected to the metalinterconnect layer 19.

Then, in step S2 in FIG. 1C, a nonmagnetic layer and a ferromagneticlayer are formed on the interlayer insulating film 21. That is, as shownin FIG. 2B, a nonmagnetic conductive film is formed on the interlayerinsulating film 21 and the contact plug 22. More specifically, thefollowing layers are sequentially formed using a sputtering method: theTa layer of, for example, 3 nm film thickness, the Al layer 25 of, forexample, film thickness 30 nm, and the Ta layer 26 of, for example, filmthickness 30 nm. The nonmagnetic conductive film is used to form aleading interconnect layer. Subsequently, a ferromagnetic layer isformed on the nonmagnetic conductive film. More specifically, thefollowing layers are sequentially formed using the sputtering method:the seed layer 31 of, for example, 3 nm film thickness, theantiferromagnetic layer 32 of, for example, 15 nm film thickness, thepinning ferrromagnetic layer 33 of, for example, 5 nm film thickness.The multilayer film including the seed layer 31, the antiferromagneticlayer 32, and the pinning ferromagnetic layer 33 is used to form apinning layer of the magneto resistive element.

Furthermore, the tunnel barrier film 29 is formed on the pinningferromagnetic layer 33 (step S3). The tunnel barrier film 29 is formed,for example, in the following manner. An Al layer of, for example, filmthickness 1 to 1.5 nm is formed on the pinning ferromagnetic layer 33using the sputtering method. The Al layer is then plasma-oxidized usingan ICP (Inductively Coupled Plasma) method. As a result, the Al layer isoxidized to form an Al₂O₃ layer forming the tunnel barrier film 29. Ofcourse, instead of oxidizing Al, it is possible to form an Al₂O₃ layeron a ferromagnetic layer using, for example, the sputtering method or aCVD (Chemical Vapor Deposition). As a result, the structure shown inFIG. 2B is completed.

Then, in step S4 in FIG. 1C, a ferromagnetic layer and a nonmagneticlayer are formed on the tunnel barrier film 29. That is, as shown inFIG. 2C, the CoFe layer 34 of, for example, 4 nm film thickness and thepermalloy layer 35 of, for example, 20 nm film thickness aresequentially formed on the tunnel barrier film 29 using the sputteringmethod. This multilayer film is used to form a free layer of the magnetoresistive element. Subsequently, a nonmagnetic conductive film is formedon the permalloy 35. Specifically, the following layers are sequentiallyformed using the sputtering method: the Ta layer 37 of, for example, 20nm film thickness, the Al layer 38 of, for example, 50 nm filmthickness, and the Ta layer 39 of, for example, 10 nm film thickness.This nonmagnetic conductive film is used to form a cap layer. As aresult, the structure shown in FIG. 2C is completed.

Then, in step S5 in FIG. 1C, a photo resist is applied to the surface ofthe nonmagnetic conductive film and is further patterned. That is, aphoto resist 50 is applied to the surface of the Ta layer 39. Then, aphotolithography technique is used to pattern the photo resist 50 sothat the resist 50 has a pattern for forming the magneto resistiveelement such as the one shown in FIG. 2D. This pattern is formed like anellipse the major axis of which extends along the direction of the easyaxis. It should be appreciated that the pattern may have other shapesuch as a rectangle.

Then, in step S6 in FIG. 1C, the nonmagnetic conductive film and theferromagnetic layer are patterned to form the cap layer 36 and the freelayer 30. That is, as shown in FIG. 2E, an etching operation isperformed by an RIE method (Reactive Ion Etching) or by Ar ion millingusing the photo resist 50 as a mask. This etching is continued until thetunnel barrier film 29 is exposed. As a result, the Ta layers 39 and 37and the Al layer 38 are patterned to form the cap layer 36. Further, thePy layer 35 and the CoFe layer 34 are patterned to form the free layer30 of the magneto resistive element.

Subsequently, the resist 50 is removed (step S7).

Then, in step S8 in FIG. 1C, an Al layer is formed. That is, as shown inFIG. 2F, an Al layer 51 of 5 nm film thickness is formed on the tunnelbarrier film 29, the free layer 30, and the cap layer 30 using thesputtering method. In this case, the Al layer 51 has a thickness ofabout 3 nm on the side of the free layer 30. The relationship betweenthe film thickness of the Al layer 51 formed on the tunnel barrier film29 and cap layer 36 and the film thickness of the Al layer 51 formed onthe sides of the free layer 30 and cap layer 36 can be varied by theconditions under which Al is formed during sputtering. For example, thisrelationship can be controlled by the distance between a target and thesemiconductor substrate, or the like.

Then, in step S9 in FIG. 1C, the Al layer is oxidized to form the Al₂O₃layer 40. That is, as shown in FIG. 2G, the Al layer 51 isplasma-oxidized using the ICP method. Thus, the Al layer 51 becomes theAl₂O₃ layer 40, and the free layer 30 and the cap layer 36 are coveredwith the Al₂O₃ layer 40.

In steps S8 and S9, the Al layer 51 is desirably formed and oxidizedwithout exposing the substrate to the atmosphere. To accomplish this, asemiconductor fabricating apparatus must be provided which cancontinuously carry out sputtering and a plasma oxidization process. Thisfabricating apparatus has, for example, a sputtering chamber and aoxidization chamber as well as a mechanism that can carry thesemiconductor substrate between these chambers without exposing it tothe atmosphere. Then, after the Al layer 51 has been formed in thesputtering chamber, the substrate is carried to the oxidization chamberwithout being removed from the semiconductor fabricating apparatus. TheAl layer 51 is then plasma-oxidized.

Then, in step S10 in FIG. 1C, the Al₂O₃ layer 40 is etched using the Arion milling or RIE method to form a side wall insulating film.Subsequently, in step S11, the tunnel barrier film 29 is etched usingthe Ar ion milling. In the present embodiment, the tunnel barrier film29 is formed of Al₂O₃, so that the Al₂O₃ layer 40 and the tunnel barrierfilm 29 can be continuously etched under similar conditions. As aresult, as shown in FIG. 2H, the Al₂O₃ layer 40 remains only on thetunnel barrier film 29 and on the side of the free layer 30 and on theside of part of the cap layer 36. Furthermore, the Al₂O₃ layer 40 isleft so as to surround the side wall of the free layer 30.

Then, in step S12 in FIG. 1C, the ferromagnetic layer is patterned toform a pinning layer. That is, the ferromagnetic layer is etched usingthe Ar ion milling or the RIE method. As a result, the pinning layer 28such as the one shown in FIG. 2I is formed. The side of the pinninglayer 28 is formed to lie flush with the side of the Al₂O₃ layer 40.Accordingly, the width of the pinning layer 28 is formed to be largerthan that of the free layer 30 by double the width of the Al₂O₃ layer40. The present steps complete the elliptic magneto resistive element 27the major axis of which extends along the direction of the easy axis. Asdescribed later, to control the adverse effects of leakage magneticfields to reduce differences in the adverse effects of leakage magneticfields among magneto resistive elements, all of the stacked film formingthe pinning layer 28 may be patterned as described above but it issufficient to pattern at least the pinning ferromagnetic layer 33 instep S12. In this case, the width of the pinning ferromagnetic layer 33is formed to be larger than that of the free layer 30 by double thewidth of the Al₂O₃ layer 40.

Then, in step S13 in FIG. 1C, a protective insulating film is formed.That is, as shown in FIG. 2J, the sputtering method or the CVD (ChemicalVapor Deposition) method is used to form the SiO₂ film 41 on the Talayer 26 so as to cover the magneto resistive element 27.

Subsequently, in step S14, a photo resist 52 is applied to the surfaceof the SiO₂ film 41. Then, the photo resist 52 is patterned using thephotolithography technique as shown in FIG. 2J.

Then, in step S15 in FIG. 1C, the SiO₂ film 41 is patterned byanisotropic etching such as the RIE method using the photo resist 52 asa mask. As a result, the protective insulating film 41 such as the oneshown in FIG. 2K is completed. Subsequently, the photo resist 52 isremoved (step S16).

Then, in step S17 in FIG. 1C, the nonmagnetic conductive film 23 ispatterned by the RIE method or ion milling using the protectiveinsulating film 41 as a mask. As a result, the leading interconnectlayer 23 such as the one shown in FIG. 2L is completed.

Subsequently, the interlayer insulating film 42 is formed on theinterlayer insulating film 21. Then, the photolithography technique orthe RIE method is used to make a contact hole that reaches the magnetoresistive element 27. Furthermore, a conductor is filled into thecontact hole to form the contact plug 43. Subsequently, the bit line 44is formed on the interlayer insulating film 42 to complete the MRAMshown in FIG. 1A.

As described above, according to the first embodiment of the presentinvention, the yield of the MRAM can be improved. This will be describedbelow.

First, the side wall insulating film 40 is formed on the sides of atleast one of the two ferromagnetic layers arranged opposite each otherwith the tunnel barrier film 29 interposed therebetween. In the presentembodiment, the side wall insulating film 40 is formed on the sides ofthe free layer 30 to surround its periphery. Accordingly, even ifresidue remains around the periphery of the magneto resistive element27, it is possible to prevent a short circuit between the pinning layer28 and the free layer 30 unless the residue is large enough to contactwith both the pinning layer 28 and the cap layer 36, located higher thanthe side wall insulating film 40. For example, in the presentembodiment, the side wall insulating film 40 has a height of about 80nm. Consequently, it is possible to hinder a short circuit between thepinning layer 28 and the free layer 30 unless the residue remainingafter the Ar ion milling is about 80 nm or more in size. With theconventional configuration, a short circuit may be caused by residue ofsize 1 to 1.5 nm, which is substantially equal to the film thickness ofthe tunnel barrier film. Therefore, the configuration according to thepresent embodiment allows the residue to be removed much more easilythan the conventional one. As a result, the yield of MRAMs, notablylarge-scale MRAMs can be effectively improved.

Further, the formation of the side wall insulating film 40 serves tohinder a short circuit between the free layer and pinning layer. Thiseliminates the need to carry out the Ar ion milling described in FIG.2I, in a diagonal direction. That is, the Ar ion milling can beaccomplished using an incident angle substantially perpendicular to thesemiconductor substrate surface. Consequently, the sides of the magnetoresistive element 27 are substantially perpendicular to thesemiconductor substrate surface. As a result, it is possible to hinder ashort circuit between the adjacent magneto resistive elements 27. Thiscontributes to improving the yield of the MRAM.

Furthermore, with the fabricating method according to the presentembodiment, the Al layer 51, formed on the side walls of the magnetoresistive element 27, is oxidized to form the side wall insulating film40. With this fabricating method, the oxidation gradually proceeds fromthe outer sides of the Al layer 51. Finally, all of the Al layer 51 isoxidized to form the Al₂O₃ layer 40. In this case, oxygen is introducedinto an end of the Al₂O₃ layer, the tunnel barrier film 29. When thefree layer 30 is patterned by the Ar ion milling, the tunnel barrierfilm 29 has its surface beaten by Ar ions and is thus damaged. As aresult, the oxygen may be lost at the end of the tunnel barrier film 29.Then, the insulating property of the Al₂O₃ layer 40 may be markedly lostto cause a short circuit between the free layer 30 and the pinning layer28. With the fabricating method according to the present embodiment,when the Al layer 51 is oxidized, oxygen is also introduced into the endof the tunnel barrier film 29. Accordingly, the Al₂O₃ layer 40 has asufficient insulating property. As a result, the free layer 30 and thepinning layer 28 can be electrically sufficiently separated from eachother. That is, it is possible to prevent a short circuit in the magnetoresistive circuit 27. Therefore, the yield of the MRAM can be improved.

Furthermore, according to the first embodiment of the present invention,the operational reliability of the MRAM is improved. This will bedescribed below.

With the fabricating method according to the present embodiment, the Arion milling described in FIG. 2I can be accomplished using an incidentangle substantially perpendicular to the semiconductor substratesurface. Accordingly, the shape of the free layer 30 in the magnetoresistive element 27 can be easily controlled. It is thus possible tohinder a value for a current required for a write from varying amongmagneto resistive elements. As a result, a write operation margin forthe MRAM can be increased to improve the operational reliability of theMRAM.

Moreover, the shape of the free layer 30 in the magneto resistiveelement 27 can be easily controlled as described above, so that it iseasy to control the horizontal extension of the pinning layer 28 withrespect to the free layer 30. It is thus possible to reduce differencesamong magneto resistive elements in the adverse effects of leakagemagnetic fields from the pinning layer 28, or the like. As a result, thewrite operation margin for the MRAM can be increased to improve theoperational reliability of the MRAM.

Now, with reference to FIGS. 3, 4A, and 4B, description will be given ofmethod of fabricating a semiconductor memory device according to asecond embodiment of the present invention. FIG. 3 is a flow chart ofMRAM fabricating steps according to the present embodiment. FIGS. 4A and4B are sectional views sequentially showing some of the fabricatingsteps. The present embodiment is used to describe another method offabricating the MRAM shown in FIGS. 1A and 1B, described in the abovefirst embodiment.

First, the structure shown in FIG. 2F is obtained through steps S1 toS8, described in the above first embodiment. Subsequently, in step S20in FIG. 3, the Al layer 51 is etched. That is, as shown in FIG. 4A, theAl layer 51 is etched using the Ar ion milling or the RIE method. As aresult, the Al layer 51 remains only on the tunnel barrier film 29 andon the sides of the free layer 30 and cap layer 36. Furthermore, the Allayer 51 is left so as to surround the periphery of the free layer 30.

Then, in step S21 in FIG. 3, the Al layer 51 is oxidized to form theAl₂O₃ layer. That is, the Al layer 51 is plasma-oxidized using, forexample, the ICP method. As a result, the side wall insulating film 40formed of an Al₂O₃ layer is completed as shown in FIG. 4B.

In the fabricating method according to the present embodiment, steps S8,S20, and S21 are also desirably executed without exposing the substrateto the atmosphere. To accomplish this, a semiconductor fabricatingapparatus must be provided which can continuously execute thesputtering, plasma oxidization process, and RIE or ion milling. Theseries of processes are executed within this semiconductor fabricatingapparatus. However, if the RIE is compared with the ion milling, theformer is more preferable.

Then, in step S11, the tunnel barrier film 29 is patterned to obtain thestructure shown in FIG. 2H. Subsequently, as in the case with the firstembodiment, steps S12 to S17 are executed to complete the MRAM shown inFIGS. 1A and 1B.

According to the present embodiment, effects similar to those of theabove first embodiment are obtained. At the same time, the operationalreliability of the MRAM can be further improved. This will be describedbelow.

With the fabricating method according to the present embodiment, afterthe Al layer 51 has been etched, it is oxidized to form the Al₂O₃ layer40. Accordingly, the step of etching the Al₂O₃ layer 40 need not beexecuted before the pinning layer 28 is patterned in contrast with thefirst embodiment. During the Ar ion milling, Al can be etched fasterthan Al₂O₃. Consequently, the etching operation can be easily stoppedonce the Ta layer 26, forming the leading interconnect layer, is exposedwhen the ferromagnetic layer is etched by the Ar ion milling in order toform the pinning layer 28. As a result, the resistance distribution ofthe leading interconnect layer 23 is improved. Furthermore, if the Al isetched using the RIE, the resistance distribution of the leadinginterconnect layer 23 can be further improved. This is because the useof the RIE enables the Al layer 51 to be selectively etched and enablesthe etching to be reliably stopped at the surface of the tunnel barrierfilm 29. In this case, only the tunnel barrier film 29 and the pinninglayer 28 must be etched by the Ar ion milling. As a result, the writeoperation margin for the MRAM can be increased to improve theoperational reliability of the MRAM.

Now, with FIGS. 5 and 6A to 6I, description will be given of method offabricating a semiconductor memory device according to a thirdembodiment of the present invention. FIG. 5 is a flow chart of MRAMfabricating steps according to the present embodiment. FIGS. 6A to 6Iare sectional views sequentially showing some of the fabricating steps.The present embodiment relates to the MRAM fabricating method accordingto the above second embodiment which uses a hard mask.

First, the structure shown in FIG. 2C is obtained through steps S1 toS4, described in the above first embodiment. Then, in step S30 in FIG.5, a hard mask layer 53 is formed on the Ta layer 39 using thesputtering or CVD method.

Then, in step S31 in FIG. 5, a photo resist is applied to the surface ofthe hard mask layer 53 and is further patterned. That is, as shown inFIG. 6B, the photolithography technique is used to pattern the photoresist 50 so that the resist 50 has a pattern for forming the magneticresistive element as in the case with the step described in step S5 inthe above first embodiment.

Then, in step S32 in FIG. 5, the hard mask layer 53 is patterned by theRIE method or Ar ion milling using the photo resist 50 as a mask.Subsequently, the photo resist 50 is removed (step S33). Subsequently,in step S34 in FIG. 5, a nonmagnetic layer (Ta layer 39 and 37 and Allayer 38) is patterned by the RIE method or Ar ion milling using thehard mask layer 53 as a mask. As a result, the cap layer 36 such as theone shown in FIG. 6C is completed.

Then, in step S35 in FIG. 5, the ferromagnetic layer is patterned toform the free layer 30. That is, as shown in FIG. 6D, an etchingoperation is performed until the tunnel barrier film 29 is exposed bythe RIE method or Ar ion milling using the hard mask layer 53 as a mask.As a result, the Py layer 35 and the Co layer 34 are patterned to formthe free layer 30 of the magneto resistive element.

Then, in step S8 in FIG. 5, an Al layer is formed. That is, as shown inFIG. 6E, the Al layer 51 of about 5 nm film thickness is formed on thetunnel barrier film 29, the free layer 30, the cap layer 36, and thehard mask layer 53 using the sputtering method. The present stepcorresponds to step S8 described in the above first embodiment.

Then, in step S20 in FIG. 5, the Al layer 51 is etched. That is, asshown in FIG. 6F, the Al layer 51 is etched using the Ar ion milling orthe RIE method. As a result, as shown in the figure, the Al layer 51remains only on the tunnel barrier film 29 and on the sides of the freelayer 30, cap layer 36, and hard mask layer 53. In particular, the Allayer 51 is left so as to surround the periphery of the free layer 30.

Then, in step S21 in FIG. 5, the Al layer 51 is oxidized to form anAl₂O₃ layer. That is, the Al layer 51 is plasma-oxidized using, forexample, the ICP method. As a result, the side wall insulating film 40formed of the Al₂O₃ layer is completed as shown in FIG. 6G.

In the fabricating method according to the present embodiment, stepsS35, S8, S20, and S21 are also desirably executed without exposing thesubstrate to the atmosphere. To accomplish this, a semiconductorfabricating apparatus must be provided which can continuously executethe sputtering, plasma oxidization process, and RIE or ion milling.

Then, in step S11 in FIG. 5, the tunnel barrier film 29 is patterned toobtain the structure shown in FIG. 6H. Subsequently, in step S12, theferromagnetic layer is patterned. As a result, the pinning layer 28 suchas the one shown in FIG. 6I is completed.

Subsequently, as described in the above first embodiment, steps S13 toS17 are executed to complete the MRAM.

With the fabricating method according to the present embodiment, effectssimilar to those of the above first and second embodiments are obtained.

FIG. 7 is a flow chart of MRAM fabricating steps according to avariation of the present embodiment. The present variation relates tothe above first embodiment which uses a hard mask layer. That is, evenwith a hard mask layer, the side wall insulating film may be formed bypatterning the Al₂O₃ layer.

Then, with reference to FIG. 8, description will be given of asemiconductor memory device according to a fourth embodiment of thepresent invention. FIG. 8 is a sectional view of a memory cell in anMRAM, notably its magneto resistive element.

As shown in the figure, the magneto resistive element 27 of the MRAMaccording to the present embodiment corresponds to the arrangementaccording to the first to third embodiments in which the composition ofAl₂O₃ as the tunnel barrier film 29 is improved. That is, the tunnelbarrier film 29 has a higher oxygen content at the end than in thecenter of the magneto resistive element 27. Specifically, thecomposition of the tunnel barrier film is Al₂O_(x) in the center of themagneto resistive element and is Al₂O_(y) at its end, where x and y areboth close to 3 and y>x.

The present structure can be formed by increasing, in the above first tothird embodiments, the time required for the oxidizing process toprovide excessive oxidization when the Al layer 51 is oxidized. Theexcessive oxidization causes oxygen to enter the tunnel barrier film 29.As a result, the oxygen content in Al₂O₃ is higher at the end of themagneto resistive element. More specifically, in the steps in FIGS. 2G,4B, and 6G, oxygen is introduced into an area of the tunnel barrier film29 which is located immediately below the in-surface edge of the freelayer 20. This enables the oxygen content in this area of the tunnelbarrier film 29 to be higher than that in the in-surface center of thefree layer 30.

With the configuration according to the present embodiment, effectssimilar to those of the above first and second embodiments are obtained.At the same time, the operational reliability of the MRAM can be furtherimproved. This will be described below.

FIG. 9A shows the planar shape of an ideal magneto resistive element.Intrinsically, the magneto resistive element is desirably perfectlyelliptic. In this case, as shown in the figure, the orientations ofspins are substantially fixed.

However, the formation of a magneto resistive element of 0.1 μm sizerequires a very difficult machining technique. Accordingly, as shown inFIG. 9B, the periphery of the magneto resistive element is actuallyprone to be somewhat notched. In such a situation, the orientations ofspins in the periphery are disturbed. Thus, the orientations of spins inthe free layer are not necessarily parallel/antiparallel with thepinning layer. For an MRAM of a Gbit class, the adverse effects in theperiphery of the MTJ element are not negligible because its magnetoresistive element is smaller. Accordingly, the MR ratio of the magnetoresistive element decreases substantially. As a result, the readoperation margin may decrease to degrade the operational reliability ofthe MRAM.

However, with the configuration according to the present embodiment, asshown in FIG. 9C, the tunnel barrier film 29 has a higher oxygen contentin the periphery of the magneto resistive element, which tends to benotched. Consequently, tunnel resistance per unit area is low in thecenter of the magnet resistive element, while it is high at the end ofthe element. That is, a tunnel current conducts easily through thecenter of the magneto resistive element but not through its end. Then,the area of the tunnel barrier film 29 which has the composition ofAl₂O_(y) does not substantially function as a magneto resistive element.The orientations of spins are prone to be disturbed in this are. Incontrast, the area of the tunnel barrier film 29 which has thecomposition of Al₂O_(x) substantially function as a magneto resistiveelement. The orientations of spins are substantially fixed in this are.This reduces the adverse effects on the MR ratio of the disturbed spinorientations at the end of the magneto resistive element. This in turnserves to provide a reliable MRAM of a Gbit class which has a large readmargin.

Now, with reference to FIG. 10, description will be given of asemiconductor memory device according to a fifth embodiment of thepresent invention. FIG. 10 is a sectional view of a memory cell in anMRAM, notably, its magneto resistive element.

As shown in this figure, the magneto resistive element 27 of the MRAMaccording to the present embodiment corresponds to the arrangementaccording to the above first to third embodiments in which the tunnelbarrier film 29 has a larger film thickness at the end of the magnetoresistive element. That is, the tunnel barrier film 29 has a filmthickness d1 in the center of the magneto resistive element and a filmthickness d2 at its end. In this case, d2>d1.

The present structure can be formed by increasing, in the above first tothird embodiments, the time required for the oxidizing process toprovide excessive oxidization when the Al layer 51 is oxidized. Theexcessive oxidization causes oxygen to enter not only the tunnel barrierfilm 29 but also an area of the in-surface edge of the free layer 30which contacts with the tunnel barrier film 29. As a result, a part ofthe CoFe layer 34, forming the free layer 30, is oxidized to form aCoO_(x) layer and an FeO_(x) layer. The CoO_(x) layer and the FeO_(x)layer are insulators and function as a part of the tunnel barrier film.That is, at the end of the magneto resistive element, the tunnel barrierfilm 29 is formed of an Al₂O₃ layer, a CoO_(x) layer, and an FeO_(x)layer. Consequently, the tunnel barrier film 29 apparently has a largerfilm thickness in the center than at the end of the magneto resistiveelement.

With the present embodiment, not only the effects described in the abovefirst and second embodiments but also the effects described in thefourth embodiment are obtained. That is, with the structure according tothe present embodiment, the tunnel barrier film 29 has a larger filmthickness in the periphery of the magneto resistive element 27, whichtends to be notched. Consequently, the tunnel resistance per unit areais low in the center of the magnet resistive element, while it is highat the end of the element. That is, a tunnel current flows easilythrough the center of the magneto resistive element but not through itsend. As a result, the effects described in the above fourth embodimentcontribute to reducing the adverse effects on the MR ratio of thedisturbed spin orientations at the end of the magneto resistive element.This in turn serves to provide a reliable MRAM having a large readmargin.

Now, with reference to FIG. 12, description will be given of asemiconductor memory device according to a sixth embodiment of thepresent invention. FIG. 12 is a sectional view of a memory cell in anMRAM, notably, its magneto resistive element.

As shown in this figure, the magneto resistive element 27 of the MRAMaccording to the present embodiment corresponds to the arrangementaccording to the above first to third embodiments in which the tunnelbarrier film 29 has a much larger film thickness at the end of themagneto resistive element. That is, the tunnel barrier film 29 has thefilm thickness d1 in the center of the magneto resistive element and afilm thickness d3 at its end. In this case, d3>d2>d1.

The present structure can be formed by increasing, in the above first tothird embodiments, the time required for the oxidizing process toprovide excessive oxidization when the Al layer 51 is oxidized. Theexcessive oxidization causes oxygen to enter not only the tunnel barrierfilm 29 but also the pinning layer 28 and the free layer 30. As aresult, a CoO_(x) layer and an FeO_(x) layer are formed by oxidizing apart of the pinning ferromagnetic layer 33, forming the pinning layer28, and a part of the CoFe layer 34, forming the free layer 30. Thus, atthe end of the magneto resistive element, the tunnel barrier film 29 isformed of an Al₂O₃ layer, and a CoO_(x) and FeO_(x) layers formed byoxidizing the CoFe layers 33 and 34. Consequently, the tunnel barrierfilm 29 apparently has a larger film thickness in the center than at theend of the magneto resistive element.

With the present embodiment, effects similar to those of the fifthembodiments are obtained. Further, the tunnel resistance at the end ofthe magneto resistive element can be further increased compared to thefifth embodiment. Therefore, the read margin can be further increased toprovide a reliable MRAM.

Now, with reference to FIG. 13, description will be given of asemiconductor memory device according to a seventh embodiment of thepresent invention. FIG. 13 is a sectional view of a memory cell in anMRAM, notably, its magneto resistive element.

As shown in the figure, the magneto resistive element 27 comprises thepinning layer 28, the tunnel barrier film 29 formed on the pinning layer28, and the free layer 30 formed on the tunnel barrier film 29. Thepinning layer 28 has a stacked structure including the seed layer 31formed of, for example, Py, the antiferromagnetic layer 32 formed of,for example, IrMn, and the pinning ferromagnetic layer 33 formed of, forexample, CoFe. Further, the free layer 30 has a multilayer structure Py35/CoFe 34. The tunnel barrier film 29 has the film thickness d1 in thecenter of the magneto resistive element and a film thickness d4 at itsend (d4>d1).

Now, with reference to FIGS. 14A and 14B, description will be given ofmethod of forming a magneto resistive element according to the presentembodiment. FIGS. 14A and 14B are sectional views sequentially showingsome of the MRAM fabricating steps.

First, the structure shown in FIG. 2D is obtained by executing steps S1to S5 in FIG. 1C, described in the above first embodiment. Then, in anAr/Cl₂ mixed gas and, for example, with the substrate temperature set at220° C., an etching operation is performed by the RIE method using thephoto resist 50 as a mask. This etching operation is continued until theTa layer 26, a part of the leading interconnect layer, is exposed. As aresult, the Ta layer 39, the Al layer 38, the Ta layer 37, the Py layer35, the CoFe layer 34, the Al₂O₃ layer 29, the pinning ferromagneticlayer 33, the antiferromagnetic layer 32, and the seed layer 31 aresequentially etched to obtain a magneto resistive element having thestructure shown in FIG. 14A. During the etching, some chloride ionsadhere to the neighborhood of end of the Al₂O₃ layer 29. Then, a verysmall amount of chloride atoms are diffused toward the inside of themagneto resistive element along the interface between the Al₂O₃ layer 29and the CoFe layers 33 and 34 owing to the substrate temperature of 220°C.

Then, the magneto resistive element is exposed to an oxidizationatmosphere. More specifically, the magneto resistive element isoxidized, for example, for about 5 minutes in an oxygen atmosphere at apressure of about 200 Torr. Then, the CoFe layers 33 and 34, arrangedover and under the tunnel barrier film 29, respectively, are oxidized ata higher speed in their areas which correspond to the end of the magnetoresistive element and which are also close to their interfaces. Thus,the structure shown in FIG. 14B is obtained.

With the configuration according to the present embodiment, in contrastwith the above first to third embodiments, the side wall insulating film40 is not formed. However, a CoO_(x) layer and an FeO_(x) layer areformed by oxidizing the CoFe layers 33 and 34, arranged over and underthe tunnel barrier film 29, respectively, in their areas correspondingto the end of the magneto resistive element. Accordingly, the tunnelbarrier film 29 is considered to have a larger film thickness at the endof the magneto resistive element. Consequently, as in the above firstembodiment, a short circuit can be hindered from occurring between thepinning layer 28 and the free layer 30 owing to residue. Further, themagneto resistive element described in FIG. 2I can be etched using anincident angle substantially perpendicular to the semiconductorsubstrate surface. It is thus possible to hinder a short circuit betweenadjacent magneto resistive elements. Furthermore, oxidization serves tosupply oxygen to the end of the Al₂O₃ layer corresponding to the end ofthe magneto resistive element. This hinders a short circuit between thepinning layer 28 and the free layer 30. As a result, the yield of theMRAM can be improved. Further, as in the above first embodiment, theoperational reliability of the MRAM can be improved.

Now, with reference to FIG. 15A, description will be given of asemiconductor memory device according to an eighth embodiment of thepresent invention. FIG. 15A is a sectional view of a memory cell in anMRAM according to the present embodiment. The present embodiment isobtained by applying the above first embodiment to a top pin type MRAM.Consequently, the structure according to the present embodiment issimilar to that described in the above first embodiment except for themagneto resistive element and its peripheral structure. Accordingly, thedescription of components similar to those of the above first embodimentis omitted.

As shown in the figure, the magneto resistive element 27 is formed onthe nonmagnetic conductive film 23, functioning as a leadinginterconnect layer. The magneto resistive element 27 is, for example, anMTJ element. The structure of the magneto resistive element 27 will bedescribed with reference to FIGS. 15A and 15B. FIG. 15B is a perspectiveview of a semiconductor memory device, focusing on the magneto resistiveelement 27.

As shown in the figures, the magneto resistive element 27 is shaped likea general ellipse the major axis of which extends along the easy axis.It includes the free layer 30 formed on the nonmagnetic conductive film23, the tunnel barrier film 29 formed on the free layer 30, and thepinning layer 28 formed on the tunnel barrier film 29. The free layer 30is formed of a stacked film including a seed layer 60 formed of Cu of,for example, film thickness 5 nm and a permalloy (Py: NiFe) layer 65 of,for example, film thickness 5 nm which are sequentially formed. Thetunnel barrier film 29 is formed of an Al₂O₃ layer of, for example, filmthickness 1 to 1.5 nm. The pinning layer 28 is formed of a stacked filmincluding a CoFe layer 61 of, for example, film thickness 1.5 nm, an Rulayer 62 of film thickness 1 nm, and a CoFe layer 63 of, for example,film thickness 2 nm which are sequentially stacked.

The free layer 30 and the tunnel barrier film 29 have substantially thesame surface area and completely overlap each other. The pinning layer28 has a smaller surface area than the free layer 30 and the tunnelbarrier film 29 and is provided, as a whole, on the tunnel barrier film29. The magneto resistive element 27 is thus formed.

An antiferromagnetic layer 64 is formed on the pinning layer 28. Theantiferroelectric layer 64 is formed of an IrMn layer of, for example,film thickness 15 nm. Furthermore, the cap layer is formed on theantiferromagnetic layer 64. The cap layer 36 is formed of a Ta layer of,for example, film thickness 5 nm. Further, the side wall insulating film40 is formed on the tunnel barrier film 29 so as to surround at leastthe periphery of the pinning layer 28. The side wall insulating film 40is formed of, for example, an Al₂O₃ film.

The other arrangements are similar to those of the first embodiment.

Now, with reference to FIGS. 15C and 16A to 16F, description will begiven of method of fabricating the semiconductor memory device shown inFIGS. 15A and 15B. FIG. 15C is a flow chart of MRAM fabricating stepsaccording to the present embodiment. FIGS. 16A to 16F are sectionalviews sequentially showing the fabricating steps. In FIGS. 16A to 16F,the structure including the metal interconnect layers 19 and 20 andother components located below them is omitted. Further, detaileddescription will be given of points different from those of thefabricating method described in the above first embodiment.

First, as described in the first embodiment, in step S1 in FIG. 15C, thestructure shown in FIG. 2A is obtained. Then, in step S40, a nonmagneticlayer, a metal layer, and a ferromagnetic layer are formed on theinterlayer insulating film 21. That is, as shown in FIG. 16A, anonmagnetic conductive film (Ta layer 26/Al layer 25/Ta layer 24) isformed on the interlayer insulating film 21 and the contact plug 22.Subsequently, a metal layer, for example, the Cu layer 60 of filmthickness 5 nm is formed on the nonmagnetic conductive film. Then, aferromagnetic layer, for example, the permalloy layer 30 of filmthickness 5 nm is formed on the metal layer 60. The metal layer 60 andthe ferromagnetic layer 65 are used to form a free layer.

Furthermore, in step S3, the tunnel barrier film 29 is formed on theferromagnetic layer 65. Subsequently, in step S41, a ferromagnetic layeris formed on the tunnel barrier film 29. That is, the CoFe layer 61 of,for example, film thickness 1.5 nm, the Ru layer 62 of, for example,film thickness 1 nm, and the CoFe layer 63 of, for example, filmthickness 2 nm are sequentially formed on the tunnel barrier film 29using the sputtering method. The ferromagnetic layer formed of themultilayer film CoFe/Ru/CoFe is used to form a pinning layer of themagneto resistive layer. Subsequently, an antiferromagnetic layer, forexample, the IrMn layer 64 of film thickness 15 nm is formed on the CoFelayer 63. Furthermore, a nonmagnetic conductive film, for example, theTa layer 36 of film thickness 5 nm is formed on the IrMn layer 64. Thisnonmagnetic conductive film 36 is used to form a cap layer. As a result,the structure shown in FIG. 16A is completed.

Then, in step S5, a photo resist is applied to the surface of thenonmagnetic conductive film 36. Then, the photolithography technique isused to pattern the photo resist so that the resist has a pattern forforming the magneto resistive element. Subsequently, in step S42, thenonmagnetic conductive film 36, the antiferromagnetic layer 64, and theferromagnetic layers 61 to 63 are patterned using the RIE method or theAr ion milling. As a result, the pinning layer 28 of the magnetoresistive element is formed as shown in FIG. 16B. Subsequently, theresist is removed (step S7).

Then, in step S8, the Al layer 51 is formed to obtain the structureshown in FIG. 16C. Subsequently, in step S9, the Al layer 51 is oxidizedto form the Al₂O₃ layer 40. As a result, the structure shown in FIG. 16Dis obtained. That is, the pinning layer 28, the antiferromagnetic layer64, and the cap layer 36 are covered with the Al₂O₃ layer 40.

Then, in step S10 in FIG. 15C, the Al₂O₃ layer 40 is etched to form aside wall insulating film. Subsequently, in step S11, the tunnel barrierfilm 29 is etched. As a result, as shown in FIG. 16E, the Al₂O₃ layer 40remains only on the tunnel barrier film 29 and on the sides of theantiferromagnetic layer 64 and pinning layer 28 and on the side of apart of the cap layer 36. Furthermore, the Al₂O₃ layer 40 is left so asto surround the periphery of the pinning layer 28 and antiferromagneticlayer 64. The Al₂O₃ layer 40 has only to surround at least the peripheryof the pinning layer 28 and need not surround the entire sides of theantiferromagnetic layer 64.

Then, in step S43, the ferromagnetic layer 65 and the metal layer 60 arepatterned. As a result, the free layer 30 is formed as shown in FIG.16F. The sides of the free layer 30 are formed so as to be flush withthe sides of the Al₂O₃ layer 40. Accordingly, the width of the freelayer 30 is formed to be larger than that of the pinning layer 28 bydouble the width of the Al₂O₃ layer 40. The present steps complete themagneto resistive element 27 shaped like an ellipse the major axis ofwhich extends along the easy axis as shown in FIG. 15B. Further, asdescribed in the first embodiment, although all of the stacked filmforming the free layer 30 may be patterned, it is sufficient to patternat least the NiFe layer 65 in step S43.

Subsequently, the structure shown in FIGS. 15A and 15B is completedthrough steps S13 to S17, described in the above first embodiment.

As described above, with the structure and fabricating method accordingto the present embodiment, effects similar to those of the above firstembodiment are obtained even with an MRAM of a top pin type structure inwhich a pinning layer is formed on a free layer.

Now, with reference to FIGS. 17, 18A, and 18B, description will be givenof method of fabricating a semiconductor memory device according to aninth embodiment of the present invention. FIG. 17 is a flow chart ofMRAM fabricating steps according to the present embodiment. FIGS. 18Aand 18B are sectional views sequentially showing some of the fabricatingsteps. The present embodiment corresponds to the above second embodimentapplied to a top pin type MRAM. It is used to describe another method offabricating the MRAM shown in FIGS. 15A and 15B, described in the aboveeighth embodiment.

First, the structure shown in FIG. 16C is obtained through steps S1 toS8 described in the above eighth embodiment. Subsequently, in step S20in FIG. 17, the Al layer 51 is etched. That is, as shown in FIG. 18A,the Al layer 51 is etched using the Ar ion milling or the RIE method. Asa result, as shown in the figures, the Al layer 51 remains only on thetunnel barrier film 29 and on the sides of the pinning layer 28,antiferromagnetic layer 64, and cap layer 36. Furthermore, the Al layer51 is left so as to surround the periphery of the pinning layer 28.

Then, in step S21, the Al layer 51 is oxidized to form an Al₂O₃ layer.As a result, as shown in FIG. 18B, the side wall insulating film 40formed of the Al₂O₃ layer is completed.

Then, in step S11, the tunnel barrier film 29 is patterned to obtain thestructure shown in FIG. 16E. Subsequently, as in the case with theeighth embodiment, the MRAM shown in FIGS. 15A and 15B is completedthrough steps S43 to S17.

With the structure and fabricating method according to the presentembodiment, the effects described in the above second embodiment areobtained even with a top pin type MRAM.

Now, with reference to FIGS. 19 and 20A to 20F, description will begiven of method of fabricating a semiconductor memory device accordingto a tenth embodiment of the present invention. FIG. 19 is a flow chartof MRAM fabricating steps according to the present embodiment. FIGS. 20Ato 20F are sectional views sequentially showing some of the fabricatingsteps. The present embodiment corresponds to the above third embodimentapplied to a top pin type MRAM.

First, the structure shown in FIG. 16A is obtained through steps S1 toS41 described in the above eighth embodiment. Then, in step S30, thehard mask layer 53 is formed on the Ta layer 36 using the sputteringmethod or the CVD method. Thus, the structure shown in FIG. 20A isobtained.

Then, in steps S31 and S32, a photo resist is applied to the surface ofthe hard mask layer 53. As shown in FIG. 20B, the lithography techniqueand etching are used to pattern the hard mask layer 53 so that the layer53 has a pattern for forming the magnetic resistive element. Thereafter,the photo resist 50 is removed (step S33). Subsequently, in step S34,the nonmagnetic layer 36 is patterned by the RIE method or Ar ionmilling using the hard mask layer 53 as a mask, to form a cap layer.Then, in step S50, the ferromagnetic layer 64 is patterned. Furthermore,the antiferromagnetic layers 61 to 63 are patterned to form the pinninglayer 28. As a result, a structure such as the one shown in FIG. 20C isobtained.

Then, in step S8, an Al layer is formed to obtain the structure shown inFIG. 20D. Subsequently, in step S20, the Al layer 51 is etched. In stepS21, the Al layer 51 is oxidized to form the Al₂O₃ layer 40. As aresult, the side wall insulating film 40 formed of the Al₂O₃ layer iscompleted as shown in FIG. 20E. The side wall insulating film 40 coversthe sides of the pinning layer 28, antiferromagnetic layer 64, cap layer36, and hard mask 53.

Then, in step S11, the tunnel barrier film 29 is patterned. Furthermore,in step S43, the ferromagnetic layer 65 and the metal layer 60 arepatterned. As a result, the free layer 30 is completed to obtain thestructure shown in FIG. 20F.

Subsequently, steps S13 to S17 are executed as described in the abovefirst embodiment to complete the MRAM.

Also with the fabricating method according to the present embodiment,effects similar to those of the above first and second embodiments areobtained even with a top pin type MRAM.

FIG. 21 is a flow chart of MRAM fabricating steps according to avariation of the present embodiment. The present variation relates tothe above first embodiment applied to a top pin type MRAM and using ahard mask layer. That is, even if a hard mask layer is used, a side wallinsulating film may be formed by patterning an Al₂O₃ film.

Now, with reference to FIG. 22, description will be given of asemiconductor memory device according to an eleventh embodiment. FIG. 22is a sectional view of a memory cell in an MRAM, notably its magnetoresistive element according to the present embodiment. The presentembodiment corresponds to the above fourth embodiment applied to a toppin type MRAM. Accordingly, its detailed description is omitted.

As shown in the figure, the magneto resistive element 27 of the MRAMaccording to the present embodiment corresponds to the arrangementaccording to the eighth to tenth embodiments in which the composition ofAl₂O₃ as the tunnel barrier film 29 is improved. That is, the tunnelbarrier film 29 has a higher oxygen content at the end than in thecenter of the magneto resistive element 27. Specifically, thecomposition of the tunnel barrier film is Al₂O_(x) in the center of themagneto resistive element and is Al₂O_(y) at its end, where x and y areboth close to 3 and y>x.

With the configuration according to the present embodiment, the effectsdescribed in the above fourth embodiment are obtained even with a toppin type MRAM.

Now, with reference to FIG. 23, description will be given of asemiconductor memory device according to a twelfth embodiment. FIG. 23is a sectional view of a memory cell in an MRAM, notably its magnetoresistive element according to the present embodiment. The presentembodiment corresponds to the above fifth embodiment applied to a toppin type MRAM. Accordingly, its detailed description is omitted.

As shown in the figure, the magneto resistive element 27 of the MRAMaccording to the present embodiment corresponds to the arrangementaccording to the above eighth to tenth embodiments in which the tunnelbarrier film 29 has a larger film thickness at the end of the magnetoresistive element. That is, the tunnel barrier film 29 has the filmthickness d1 in the center of the magneto resistive element and the filmthickness d2 at its end. In this case, d2>d1.

The present structure can be formed by increasing, in the above eighthto tenth embodiments, the time required for the oxidizing process toprovide excessive oxidization when the Al layer 51 is oxidized. Theexcessive oxidization causes oxygen to enter not only the Al₂O₃ layer 29but also an area of the in-surface edge of the pinning layer 28 whichcontacts with the tunnel barrier film 29. As a result, a part of theCoFe layer 61, forming the pinning layer 30, is oxidized to form aCoO_(x) layer and an FeO_(x) layer. That is, at the end of the magnetoresistive element, the tunnel barrier film 29 is formed of an Al₂O₃layer, a CoO_(x) layer, and an FeO_(x) layer. Consequently, the tunnelbarrier film 29 apparently has a larger film thickness in the centerthan at the end of the magneto resistive element.

With the above configuration, the effects described in the above fifthembodiment are obtained even with a top pin type MRAM.

Now, with reference to FIG. 24, description will be given of asemiconductor memory device according to a thirteenth embodiment. FIG.24 is a sectional view of a memory cell in an MRAM, notably its magnetoresistive element according to the present embodiment. The presentembodiment corresponds to the above sixth embodiment applied to a toppin type MRAM. Accordingly, its detailed description is omitted.

As shown in this figure, the magneto resistive element 27 of the MRAMaccording to the present embodiment corresponds to the arrangementaccording to the above eighth to tenth embodiments in which the tunnelbarrier film 29 has a much larger film thickness at the end of themagneto resistive element.

The present structure can be formed by increasing, in the above eighthto tenth embodiments, the time required for the oxidizing process toprovide excessive oxidization when the Al layer 51 is oxidized. Theexcessive oxidization causes oxygen to enter not only the Al₂O₃ layer 29but also the pinning layer 28 and the free layer 30. As a result, a partof the CoFe layer 34, forming the free layer 30, is oxidized to form aCoO_(x) layer and an FeO_(x) layer. Further, a part of the NiFe layer65, forming the free layer 30, is oxidized to form an NiFe oxide film.Thus, at the end of the magneto resistive element, the tunnel barrierfilm 29 is formed of an Al₂O₃ layer, and an insulating film formed byoxidizing the CoFe layer 61 and NiFe layer 65. Consequently, the tunnelbarrier film 29 apparently has a larger film thickness in the centerthan at the end of the magneto resistive element.

According to the present embodiment, effects similar to those of theabove sixth embodiment are obtained even with a top pin type MRAM.

Now, with reference to FIG. 25, description will be given of asemiconductor memory device according to a fourteenth embodiment. FIG.25 is a sectional view of a memory cell in an MRAM, notably its magnetoresistive element according to the present embodiment. The presentembodiment corresponds to the above seventh embodiment applied to a toppin type MRAM.

As shown in the figure, the magneto resistive element 27 comprises thefree layer 30, the tunnel barrier film 29 formed on the free layer 30,and the pinning layer 28 formed on the tunnel barrier film 29. The freelayer 30 has a stacked structure including the seed layer 60 formed of,for example, Cu and the ferromagnetic layer 30 formed of, for example,Py. The pinning layer 28 also has a stacked structure including, forexample, the CoFe layer 61, the Ru layer 62, and the CoFe layer 63,which are sequentially formed. The tunnel barrier film 29 has the filmthickness d1 in the center of the magneto resistive element and the filmthickness d4 at its end (d4>d1).

A method of forming the magneto resistive element according to thepresent embodiment is similar to that of the above seventh embodiment.That is, the structure shown in FIG. 16B is obtained through steps S1 toS42 in FIG. 15C, described in the above eighth embodiment. Subsequently,the tunnel barrier film 29, the ferromagnetic layer 30, and the metallayer 60 are sequentially etched. Then, the magneto resistive element isexposed to an oxygen atmosphere. As a result, the CoFe layers 61 andpermalloy layer 65, arranged over and under the tunnel barrier film 29,respectively, are oxidized in their areas corresponding to the end ofthe magneto resistive element. Thus, the structure shown in FIG. 25 isobtained.

According to the present embodiment, effects similar to those of theabove seventh embodiment are obtained even with a top pin type MRAM.

Now, with reference to FIG. 26A, description will be given of method offabricating a semiconductor memory device according to a fifteenthembodiment of the present invention. FIG. 26A is a flow chart of MRAMfabricating steps according to the present embodiment.

As shown in the figure, the fabricating method according to the presentembodiment corresponds to the fabricating steps described in the abovefirst embodiment, variation of the third embodiment, eighth embodiment,and variation of the tenth embodiment wherein the Al layer is oxidizedin step S9 and then annealed in step S60.

The fabricating method according to the present embodiment improves theinsulating property of the side wall insulating film 40. The Al₂O₃ filmforming the side wall insulating film 40 may have the loss of oxygen orinclude an area with an excessive amount of Al or oxygen. However, byoxidizing and then annealing the Al layer as in the present embodiment,Al and oxygen atoms can be made uniform. As a result, the insulatingproperty of the Al₂O₃ can be improved. Further, once the Al layer isoxidized, the composition of the resultant side wall insulating film isnot completely Al₂O₃. However, the annealing operation helps completethe composition of the side wall insulating film. Therefore, theinsulating property is improved.

FIG. 26B is a flow chart showing some MRAM fabricating steps accordingto a variation of the present embodiment. The present variationcorresponds to the fabricating steps described in the above second,third, ninth, and tenth embodiments wherein the Al layer is oxidized instep S21 and then annealed in step S60. The above effects are alsoobtained using a fabricating method according to the present variation.The annealing in step S60 may be carried out at any time after the Allayer oxidizing step and need not necessarily be executed immediatelyafter the oxidizing step. Further, the annealing step may becontinuously executed with the Al layer forming and oxidizing steps andother steps within the same fabricating apparatus.

As described above, according to the first to sixth embodiments of thepresent invention, the side wall insulating wall 40 is formed on thetunnel barrier film 29 so as to surround the periphery of the free layer30. It is thus possible to hinder a short circuit between the pinninglayer 28 and the free layer 30 caused by residue resulting from the Arion milling. Further, since the side wall insulating film 40 prevents ashort circuit between the pinning layer 28 and the free layer 30, ionscan enter the semiconductor substrate surface substantiallyperpendicularly to it during the Ar ion milling step executed to formthe pinning layer 28. Thus, the shape of the pinning layer 28 can beeasily controlled to ensure a sufficient operation margin for the MRAM.Furthermore, the side wall insulating film 40 is formed by oxidizing theAl layer 51. In this case, oxygen is also supplied to the end of thetunnel barrier film 29. Consequently, those areas of the tunnel barrierfilm 29 which correspond to the ends of the magneto resistive elementcan sufficiently maintain their insulating property. This makes itpossible to prevent a short circuit between the pinning layer 28 and thefree layer 30.

Further, according to the seventh and fourteenth embodiments, a part ofthe pinning layer 28 and free layer 30 are oxidized. As a result, thetunnel barrier film 29 has a larger film thickness at the end of themagneto resistive element, thus producing the above effects.

Furthermore, according to the eighth to thirteenth embodiments, effectssimilar to those of the above first to sixth embodiments are obtainedeven with a top pin type MRAM. That is, the side wall insulating film 40is formed on the tunnel barrier film 29 so as to surround the peripheryof the pinning layer 28. It is thus possible to prevent a short circuitbetween the pinning layer 28 and the free layer 30. Further, ions canenter the semiconductor substrate surface substantially perpendicularlyto it during the Ar ion milling step executed to form the free layer 30.Thus, the shape of the free layer 30 can be easily controlled to ensurea sufficient operation margin for the MRAM.

Furthermore, according to the fifteenth embodiment, the Al layer 51 isoxidized and then annealed. This results in the uniform composition ofthe Al₂O₃ layer forming the side wall insulating film 40. Thus, theinsulating property of the side wall insulating film 40 can be improved.

In the description of the above embodiments, Al is cited as an exampleof material used to form the side wall insulating film 40. However, thepresent embodiment is not particularly limited to Al. Other metal oralloy may be used. Preferably, it is desirable to use material that iseasier to oxidize than the ferromagnetic material used for the freelayer or the pinning layer. Further, the formation of the side wallinsulating film 40 is not limited to oxidization. For example,nitridization or fluoridization may be used. However, in view of theyield and manufacturing costs, the side wall insulating film 40 and thetunnel barrier film 29 are desirably an oxide, a nitride, or a fluoridecontaining the same metal element. For example, Al₂O₃, AlN, MgO, HfO₂,GaO, LaAlO₃, MgF₂, CaF₂, or the like may be used. These compounds mayhave a small loss of oxygen (nitrogen or fluorine). Further, the abovefabricating steps are not limited to the above order. The order can bechanged as drastically as possible. Furthermore, in the description ofthe above eighth to thirteenth embodiments, the pinning layer 28 has amultilayer structure including the CoFe layers 61 and 63 and the Rulayer 62. However, the pinning layer 28 may be formed only of a CoFelayer.

Further, in the description of the above embodiments, the magnetoresistive element is a memory cell using an MTJ element. However, a GMR(Giant Magneto Resistive) element, a CMR (Colossal Magneto Resistive)element, or the like may be used.

Various applications are possible in magneto resistive random accessmemories (semiconductor memory) according to the first to fifteenthembodiments of the present invention. FIGS. 27 to 33 show some examplesof applications thereof.

APPLICATION EXAMPLE 1

As an example, FIG. 27 shows a DSL data path part of a modem for adigital subscriber line (DSL). The modem comprises a programmabledigital signal processor (DSP) 100, an analogue-digital converter 110, adigital-analogue converter 120, filters 130 and 140, a transmissiondriver 150, and a receiver amplifier 160. In the structure of FIG. 27, aband-pass filter is omitted. Instead, it includes, as optional memoriesof various types which can hold line code programs, a magneto resistiverandom access memory 170 according to the first to fifteenth embodimentsof the present invention, and an EEPROM 180.

In this example, two memories of the magneto resistive random accessmemory and EEPROM are used as memories for holding the line codeprograms. However, the EEPROM may be replaced by another magnetoresistive random access memory. Further, only a magneto resistive randomaccess memory may be used, instead of using two memories.

APPLICATION EXAMPLE 2

As another example, FIG. 28 shows a part of realizing a communicationfunction in a cellular phone terminal. As shown in FIG. 28, the part ofrealizing a communication function comprises a transmission/receptionantenna 201, an antenna sharing device 202, a receiving section 203, abase band processing section 204, a DSP (Digital Signal Processor) 205used as a voice codec, a speaker (receiver) 206, a microphone(transmitter) 207, a transmitting section 208, and a frequencysynthesizer 209.

Further, as shown in FIG. 28, the cellular phone terminal 300 isprovided with a control section 200 which controls sections of thecellular phone terminal. The control section 200 is a microcomputerformed by connecting a CPU 221, a ROM 222, a magneto resistive randomaccess memory (MRAM) 223 according to the first to fifteenth embodimentsof the present invention, and a flash memory 224 through a CPU bus 225.Some programs to be executed in the CPU 221 and necessary data such asfonts for display are prestored in the ROM 222. Further, the MRAM 223 ismainly used as a work space. For example, the MRAM 223 is used forstoring data which is being calculated according to necessity when theCPU 221 is executing a program, or for temporarily storing data to betransmitted and received among the sections. The flash memory 224 storessetting parameters, in the case of adopting a method of use in which thesetting conditions just before turning off the power of the cellularphone terminal 300 is stored and the same setting conditions are usedwhen the terminal is turned on next. Specifically, the flash memory 224is a non-volatile memory, in which the stored data is not erased byturning off the power of the cellular phone terminal.

Although the ROM 222, MRAM 223, and flash memory 224 are used in thisapplication example, the flask memory 224 may be replaced by a magnetoresistive random access memory according to the first to fifteenthembodiments of the present invention. Further, the ROM 222 may also bereplaced by a magneto resistive random access memory according to thefirst to fifteenth embodiments of the present invention.

APPLICATION EXAMPLE 3

FIG. 29 to 33 show an example in which a magneto resistive random accessmemory according to the first to fifteenth embodiments of the presentinvention is applied to a card (MRAM card), such as a smart media, whichstores media contents.

In FIG. 29, an MRAM card 400 comprises an MRAM chip 401, an openingportion 402, a shutter 403, and an external terminal 404. The MRAM chip401 is contained inside the card main body 400, and is exposed to theoutside through the opening portion 402. When the MRAM card is carried,the MRAM chip 401 is covered with the shutter 403. The shutter 403 isformed of a material having an effect of shielding the chip from anexternal magnetic field, such as ceramic. When the data in the card istransferred, the shutter 403 is opened and the MRAM chip 401 is exposed.The external terminal 404 is used for taking out the contents datastored in the MRAM card to the exterior.

FIGS. 30 and 31 are a top view and a sectional view of a transfer devicewhich transfers data to the MRAM card. The transfer device is acard-inserting type transfer device. A second MRAM card 450 which an enduser uses is inserted in an inserting section 510 of the transfer device500, and pushed into the device until it is stopped by a stopper 520.The stopper 520 is also used as a member for positioning the first MRAM550 and the second MRAM card. Simultaneously with positioning the secondMRAM card 450 to a predetermined position, data stored in the first MRAMcard is transferred to the second MRAM card.

FIG. 32 shows a fit-in type transfer device. In this type, a second MRAMcard is mounted on a first MRAM against the stopper 520, as shown in anarrow in FIG. 32, such that the second MRAM card is fitted on the firstMRAM. The transfer method thereof is the same as that of thecard-inserting type, and its explanation is omitted.

FIG. 33 shows a slide-type transfer device. In this type, a receiverslide 560 is provided on a transfer device 500, in the same manner as aCD-ROM drive and a DVD drive. The receiver slide 560 is moved as shownby an arrow in FIG. 33. When the receiver slide 560 has been moved tothe state as shown by a broken line in FIG. 33, a second MRAM card 450is placed on the receiver slide 560, and the receiver slide 560 carriesthe second MRAM card into the transfer device 500. The slide-type deviceis the same as the card-insertion type in the point that the second MRAMcard is carried such that a distal end portion of the second MRAM cardabuts against the stopper 520 and in the transfer method. Therefore,their explanations are omitted.

In the embodiments described above, the side wall insulating film 40covers either side of the pinning layer 28 or free layer 30 entirely.Nonetheless, the sides of the layer 28 or layer 30 need not be entirelycovered.

If the free layer 30 provided on the tunnel barrier film 29 is thick,the insulating film 40 may cover only a part of the side of the freelayer 30 as shown in FIG. 34. More precisely, the film 40 may cover onlythe lower part of the side of the layer 30, which lies near the tunnelbarrier film 29. Thus, the film 40 does not cover the upper part of theside of the layer 30.

In the case of the top pin type MRAM, the insulating film 40 may coveronly a part of the side of the pinning layer 28 as illustrated in FIG.35. More specifically, the film 40 may cover only the lower part of theside of the pinning layer 28, which lies near the tunnel barrier film29.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A semiconductor memory device comprising: a memory cell comprising afirst ferromagnetic film, a tunnel barrier film formed on the firstferromagnetic film, and a second ferromagnetic film formed on the tunnelbarrier film; a side wall insulating film formed so as to surround atleast sides of the second ferromagnetic film; and an interlayerinsulating film formed so as to cover the memory cell and the side wallinsulating film, wherein the tunnel barrier film has a higher oxygencontent in an in-surface edge portion than in an in-surface centralportion.
 2. The device according to claim 1, wherein the side wallinsulating film contacts with the tunnel barrier film. 3-4. (canceled)5. The device according to claim 1, wherein the side wall insulatingfilm is formed of aluminum oxide.
 6. The device according to claim 1,wherein the side wall insulating film and the tunnel barrier filmcontain a common metal element.
 7. The device according to claim 1,wherein the side wall insulating film and the tunnel barrier film areboth formed of aluminum oxide.
 8. The device according to claim 1,wherein the side wall insulating film contacts with at least a part ofside wall of the tunnel barrier film along a circumferential direction.9. The device according to claim 1, wherein the tunnel barrier film isformed of aluminum oxide.
 10. A semiconductor memory device comprising:a memory cell comprising a first ferromagnetic film, a tunnel barrierfilm formed on the first ferromagnetic film, and a second ferromagneticfilm formed on the tunnel barrier film; and a side wall insulating filmformed so as to surround at least sides of the second ferromagnetic filmand containing a metal element, wherein the tunnel barrier film has ahigher oxygen content in an in-surface edge portion than in anin-surface central portion.
 11. The device according to claim 10,wherein the side wall insulating film contacts with the tunnel barrierfilm. 12-13. (canceled)
 14. The device according to claim 10, whereinthe side wall insulating film is formed of aluminum oxide.
 15. Thedevice according to claim 10, wherein the side wall insulating film andthe tunnel barrier film contain a common metal element.
 16. The deviceaccording to claim 10, wherein the side wall insulating film and thetunnel barrier film are both formed of aluminum oxide.
 17. The deviceaccording to claim 10, wherein the side wall insulating film contactswith at least a part of side wall of the tunnel barrier film along acircumferential direction.
 18. The device according to claim 10, whereinthe tunnel barrier film is formed of aluminum oxide.
 19. A semiconductormemory device comprising: a memory cell comprising a first ferromagneticfilm, a tunnel barrier film formed on the first ferromagnetic film, anda second ferromagnetic film formed on the tunnel barrier film; and aside wall insulating film formed on the tunnel barrier film so as tosurround a periphery of the second ferromagnetic film, wherein thetunnel barrier film has a higher oxygen content in an in-surface edgeportion than in an in-surface central portion. 20-21. (canceled)
 22. Thedevice according to claim 19, wherein the side wall insulating film isformed of aluminum oxide.
 23. The device according to claim 19, whereinthe side wall insulating film and the tunnel barrier film contain acommon metal element.
 24. The device according to claim 19, wherein theside wall insulating film and the tunnel barrier film are both formed ofaluminum oxide.
 25. The device according to claim 19, wherein the sidewall insulating film contacts with at least a part of side wall of thetunnel barrier film along a circumferential direction.
 26. The deviceaccording to claim 19, wherein the tunnel barrier film is formed ofaluminum oxide.
 27. A semiconductor memory device comprising: a memorycell comprising a first ferromagnetic film, a tunnel barrier film formedon the first ferromagnetic film and containing oxygen elements, and asecond ferromagnetic film formed on the tunnel barrier film, the tunnelbarrier film having a larger tunnel resistance per unit area in anin-surface edge portion than in an in-surface central portion.
 28. Thedevice according to claim 27, wherein the tunnel barrier film has ahigher oxygen content in the in-surface edge portion than in thein-surface central portion.
 29. (canceled)
 30. The device according toclaim 27, wherein the tunnel barrier film comprises in the in-surfaceedge portion a magnetic metal element contained in at least one of thefirst and second magnetic films.
 31. The device according to claim 27,wherein the tunnel barrier film is formed of aluminum oxide. 32-52.(canceled)